A floor of a vehicle body (hereinafter, referred to just as a “floor”) is not only primary responsible for torsional rigidity and bending rigidity of a vehicle body at a vehicle traveling time, but also responsible for transfer of an impact load during crash, further it largely affects on a weight of the vehicle body, and therefore, it is required to include antinomy characteristics of both high rigidity and light weight. The floor includes planar panels (for example, a dash panel, a front floor panel, a rear floor panel, and so on) which are welded to be joined with each other, long members (for example, a floor cross member, a seat cross member, and so on) having approximately groove-shaped cross sections which are fixed to be disposed in a vehicle width direction of these planar panels by welding to enhance rigidity and strength of the floor, and long members (a side sill, a side member, and so on) having approximately groove-shaped cross sections which are fixed to be disposed in a vehicle forward and backward direction to enhance the rigidity and the strength of the floor. For example, the floor cross member is normally joined to other members such as, for example, a tunnel part of the front floor panel and the side sill via outward flanges formed at both end parts in a longitudinal direction.
FIG. 12A, FIG. 12B are explanatory views illustrating a floor cross member 1. FIG. 12A is a perspective view, and FIG. 12B is a XII arrow view in FIG. 12A.
In general, the floor cross member 1 is joined to an upper surface (a surface at an interior side) of a front floor panel 2. A floor is reinforced by this floor cross member 1 coupling a tunnel part (not-illustrated) formed by bulging at approximately a center in a width direction of the front floor panel 2 and side sills 3 spot-welded at both side parts in a width direction of the front floor panel 2. The floor cross member 1 has approximately a groove-shaped cross section, and it is spot-welded to the tunnel part and the side sills 3 via outward flanges 4 formed at both end parts in a longitudinal direction thereof, and thereby, rigidity of the floor and a load transfer characteristic when an impact load is applied improve.
FIG. 13A and FIG. 13B are explanatory views schematically illustrating a conventional press-forming method of the floor cross member 1. FIG. 13A is the explanatory view schematically illustrating drawing in which forming is performed while applying a binding force at an end of a material by a blank holder. FIG. 13B is the explanatory view schematically illustrating bend-forming using a developed blank 6.
In the press-forming by the drawing illustrated in FIG. 13A, an excess part 5a is formed at a press-forming material 5, the excess part 5a is cut along a cutting-line 5b, and thereafter, a flange 5c is stood up. Besides, in the press-forming by the bend-forming illustrated in FIG. 13B, the press-forming by the bend-forming is performed for the developed blank 6 having a developed blank shape. The floor cross member 1 is conventionally formed by performing the press-forming by the drawing illustrated in FIG. 13A or the press-forming by the bend-forming illustrated in FIG. 13B. From a point of view of improving material yield, the press-forming by the bend-forming is preferable than the press-forming by the drawing accompanied by the cutting of the excess part 5a. 
The floor cross member 1 is an important structural member which is responsible for the rigidity improvement of the vehicle body and absorption of the impact load during side crash (side impact). Accordingly, in recent years, a thinner and higher strength high-tensile strength steel sheet, for example, a high-tensile strength steel sheet with a tensile strength of 390 MPa or more (a high-strength steel sheet or a HSS [high tensile strength steel]) has been used as a material of the floor cross member 1 from a point of view of reduction in weight and improvement in crash safety. However, formability of the high-tensile strength steel sheet is not good, and therefore, it is a problem that flexibility of design of the floor cross member 1 is low.
It is concretely described with reference to FIG. 12A and FIG. 12B. It is desirable to form the continuous outward flange 4 at a whole periphery of an end part of the floor cross member 1, and to obtain a flange width with a certain degree of length to enhance joining strength and torsional rigidity between the floor cross member 1 and the tunnel part of the front floor panel 2, the side sills 3, and to enhance the rigidity of the floor and the load transfer characteristic during crash.
However, it is difficult to obtain a desired shape when the continuous outward flange 4 is formed at the whole periphery of the end part of the floor cross member 1, and to obtain the flange width with the certain degree of length because basically, stretch flange cracks at a flange part corresponding to an outer periphery of a ridge line part of the outward flange 4 (hereinafter, referred to as a “ridge line part flange portion”) and wrinkling at a proximity part 1b of the outward flange 4 at a ridge line part 1a occur. These forming failures are easy to occur as a material strength of the floor cross member 1 is higher, and as a stretch flange rate at the forming of a ridge line part flange portion 4a of the outward flange 4 is higher (namely, for example, as a cross sectional wall angle θ in FIG. 12B is steeper, or as a flange height is higher).
The floor cross member 1 tends to be high-strengthened to reduce the weight of the vehicle body, and tends to be designed to a shape with high stretch flange rate from a point of view of performance thereof and a joint part shape with other members, and therefore, the forming of the continuous outward flange 4 including the ridge line part flange portion 4a is difficult to be enabled by the conventional press-forming method. Accordingly, it is the present situation in which cutouts cannot but be provided at the ridge line part flange portion 4a of the outward flange 4 of the floor cross member 1 made up of the high-tensile strength steel sheet as illustrated in FIG. 12A and FIG. 12B from restrictions on the press-forming technology as stated above even if lowering of the performance of the floor cross member 1 is accepted.
In Patent Literatures 1 to 3, the inventions are disclosed, in which a shape fixability failure in a high-strength material press-forming product is solved by devising a pad mechanism of a metal forming-tool though it is not intended for the forming of the floor cross member 1. These inventions are ones in which deflection is intentionally generated at a material during the forming by a positional relationship of the pad pressing at least a portion of a part (groove bottom part) where a punch top part and a punch top part face with each other, to thereby enable improvement in the shape fixability after the forming.